A selector lever of an automatic transmission system is typically allowed to be shifted to any one of a number of ranges which, for instance, may include park (P), reverse (R), neutral (N), fourth drive (D4), third drive (D3), and second drive (2) ranges. In a typical stick shift arrangement, a selector lever projects upright from a floor panel, and can be freely shifted between N, D4 and D3 at will. However, in order to shift the selector lever between R and P, from N to P and from D3 to 2, it is necessary to push a release knob provided in the selector lever handle, and disengage a lock pin which normally engages a cam plate secured to a pivot center of the selector lever.
Also, a selector lever of an automatic transmission system is normally provided with a shift lock mechanism which allows the release knob to be depressed only when the brake pedal is pressed if the selector lever is in the park range. In other words, the shift lock mechanism prohibits the selector lever to be shifted from the park range unless the brake pedal is pressed. For instance, Japanese patent laid open publication No. 64-12920 discloses a typical shift lock mechanism.
In the case of a stick shift type selector lever, the shift lock mechanism is not required to have a very high mechanical strength because preventing the movement of the release knob is sufficient, and it does not require any strong force. However, in the case of a column shift type selector lever, no release knob is used, and the same function is accomplished by the pivoting or tilting movement of the selector lever in the axial direction of the steering column. In other words, when the vehicle operator wishes to move the selector lever, for instance, from the park range to the drive range, he pulls the grip handle of the selector lever toward him, and achieves the necessary releasing action. Therefore, the force applied by the vehicle operator to the selector lever will be magnified at the base end of the selector lever by a lever action, and a substantial mechanical strength would be required for the shift lock mechanism intended for prohibiting such a releasing movement of the selector lever.
However, a high mechanical strength of the shift lock mechanism is difficult to achieve because the entire assembly of the shift lock mechanism must be installed in a small mounting space allocated on the steering column. Any protrusion on the steering column would be highly undesirable because it is a highly conspicuous location in the passenger compartment of the vehicle.